Prestressed girder



July 12, 1966 a. e. GREULICH PRESTRESSED GIRDER 2 Sheets-Sheet 1Original Filed May 2, 1962 a H y T U Jar 0 mdmmuw m M M w w m 6 1. Amwww; w n M M mh 0000c 0000 no 0000 L T Ill: i w H... QM E E N July 12,1966 Original Filed May 2, 1962 G. G. GREULICH PRESTRESSED GIRDER 2Sheets-Sheet 2 o o o o 2 s I w LL INVENTOR 659440 6. GQEz/A Kb BY WMMATTOPNEYS.

United States Patent 3,260,024 PRESTRESSE'D GIRDER Gerald GregoryGreulich, 3018 NE. 20th Court, Fort Lauderdale, Fla.

Original application May 2, 1962, Ser. No. 191,966, now Patent No.3,166,830, dated Jan. 26, 1965. Divided and this application Dec. 27,1963, Ser. No. 333,880

6 Claims. (Cl. 52-223) This invention relates to prestressed girders,and more particularly to one in which only the top chord is made fromprestressed concrete. This application is a division of my copendingapplication, Serial Number 191,966, filed May 2, 1962, now Patent No.3,166,830.

Prestressed concrete construction has attained its present acceptanceand widespread use because, by reducing dead loads or permitting the useof larger clear spans with the same dead load or weight, as well asgreater stiffness of construction with less deflection, a less costlyand more flexible building design is possible. It is also known thatbecause prestressing uses concrete more fully, .less of it is requiredfor a given loading condition so that the benefits of a lighter buildingare obtained Without sacrificing strength or rigidity. Lower overallweight naturally reduces column and foundation size requirements, withattendant reduction in their costs. The factor of lower deflection alsoreduces problems of fitting long rows of window frames or prefabricatedpartitions into buildings. Nevertheless, in spite of all of theseadvantages, prestressed concrete beams and girders are very heavy totransport and handle, while it is quite an undertaking to do theprestressing at the site of the construction.

It is among the objects of this invention to provide a prestressedgirder which is relatively easy to make, which can be constructed eitherat the prestressing plant or at the building site, and which expeditesbuilding.

- In accordance with this invention only the top chord of a girder ismade from prestressed concrete. It is made separately from the rest ofthe girder before the girder is assembled. Also in a separate operationa metal web is secured to a metal bottom chord. Then the bottom chord,and preferably at least part of the web, are stretched lengthwise insuitable apparatus. While the bottom chord is maintained in itsstretched condition, the metal web is rigidly secured to the top chord,such as to gusset plate means projecting from the concrete. Then thestretching apparatus is disconnected from the bottom chord and thegirder is complete. The concrete upper chord of the girder is undermaterial compression, due to the prestressing, -and the lower chord isunder material tension because of the pretensioning which is maintainedby the web.

The invention is illustrated in the accompanying drawings, in which FIG.1 is a side view of the top chord of my girder in inverted position inprestressing apparatus;

FIG. 2 is a side view of the finished top chord right side up, with aportion broken away in section;

FIG. 3 is an enlarged cross section of the top chord taken on the lineIIIIII of FIG. 2;

FIG. 4 is a side view of the bottom chord and the Web secured to it;

FIG. 5 is an enlarged cross section taken on the line V-V of FIG. 4;

3,266,024 Patented July 12, 1966 FIG. 6 is a side view of the elementsof the girder inverted in apparatus for prestressing the bottom chord;

FIG. 7 is a fragmentary side view of the finished girder;

FIG. 8 is a view similar to FIG. 7 of a modification; and

FIG. 9 is a vertical section taken on the line IX--IX of FIG. 8.

The top chord for my girder is made by molding concrete into the desiredshape around cables or rods, hereinafter called tendons. The tendons aredisposed side by side in the mold and their ends are fastened tosuitable tension jacks. Before or after the concrete has been poured inthe mold the jacks are actuated to stretch the tendons short of theirelastic limit, and they are held in that condition until after theconcrete sets. Then the tendons are released from the jacks, and theirtendency to contra-ct places the concrete under compression to form aprestressed chord. In FIG. 1 of the drawings, some of the apparatuswhich can be used for carrying out this method is shown. It includesjacks I mounted in horiz-ontally spaced anchor members 2 that may beheld a fixed distance apart by a horizontal beam 3 joined to their lowerends. Each anchor member supports one or more rows of the jacks, whichare detachably secured in any suitable manner to the opposite ends of aplurality of parallel tendons 4. If desired, the jacks can be eliminatedat one end and their places taken by fixed clamps. The drawing shows thetop chord after the concrete 5 has set and the forms have been removed,but before the tendons have been released from the jacks. The chord isbottom side up.

To enable the web of the girder to be readily connected to the concretetop chord, it is preferred that at the time of molding the chord a lineof upwardly projecting metal gusset plates 6 should be embedded in theconcrete. To help anchor the plates in the concrete, they may beprovided with holes, through which extend dowel pins 7 that are likewiseembedded in the concrete as shown in FIGS. 2 and 3. After the concretehas set, the jacks are released from the tendons, which then will tendto contract to their original length. In doing so, they will compressthe concrete lengthwise of the chord and thereby form a prestressed topchord for a girder. The projecting ends of the tendons will be cut offflush with the ends of the concrete member.

In an entirely separate operation, the web of the girder is secured tothe bottom chord. Both of these parts are all metal. The web and chordmay take various wellknown forms, a very suitable form being shown inFIGS. 4 and 5. It will there be seen that the bottom chord is formedfrom parallel angle .bars 10 riveted or welded to the opposite sides ofa line of gusset plates 11. The web is formed from short angle bars 12,preferably arranged in pairs, riveted or welded at one end to theopposite sides of the gusset plates. Some of the bars are vertical andsome are inclined, the inclined bars at one side of the center of theweb being inc-lined opposite to those at the other side of the center ofthe web. In the finished girder the vertical bars usually will becompres sion members and the inclined bars usually will be tensionmembers. a

The next step is to secure the web bars 12 to the gusset plates 6 of thetop chord. This is done by placing the inverted top chord on a suitablesupport, such as a long rigid beam or platform 13 having anchor members14 at its opposite ends. Mounted in one of the anchor members near itstop is a pulling jack 15, while a similar jack 16 or a rigid clamp ismounted in the other anchor member. They are clamped to the adjoiningends of the bottom chord, which is held by them in inverted positionwith the web bars extending down and straddling the lower row of gussetplates 6- projecting from the inverted top chord. Before fastening thelower ends of the web bars to the .adjoining gusset plates, the jack orjacks are actuated to stretch the chord bars 10 and hold them undertension. This spreads the lower ends of the web bars farther apart.While the bottom chord of the girder is held in tension in this way, theweb bars are riveted or welded to the lower gusset plates to form acomplete girder.

It will be seen that when the bottom chord subsequently is released fromthe tensioning means, its longitudinal contraction will be restrainedand largely prevented by the inclined web tension bars pulling againstthe prestressed top chord at their lower ends. The same action causesthe inclined bars to help tendons 4 hold the top chord underlongitudinal compression. When the girder is removed from the tensioningapparatus and turned right side up, it will appear as shown in FIG. 7,with a presetressed (compressed) top chord and a prestressed (tensioned)bottom chord. As has just been explained, both chords of the girder wereprestressed before they were connected together. The resulting girderwill'be much stronger than an ordinary girder and therefore can be usedin longer lengths without intermediate support. The components of thegirder will not change their lengths appreciably until loads greaterthan design loads are applied to them. Also, due to the greatly reduceddeflection in such a prestressed girder, shallower girder depths can beused, thereby reducing the overall heights of buildings whilemaintaining the same clearance between floor and ceiling.

Girder deflection under load can be reduced still further by elongatingthe inclined web bars before fastening their free ends to the top chord.The elongating can be done by applying heat in any suitable manner tothe bars throughout their lengths. At the same time, where possible, itwould be desirable to shorten the vertical web bars by chilling themthroughout their lengths. While the web bars are longitudinally expandedand contracted in this manner, their free ends are secured to the gussetplates of the top chord. Then, when the web returns to room temperature,the inclined bars will be under greater .tension than otherwise and thevertical bars will be under greater compression. Consequently,deflections under load, due to the web changing its dimensions, will beeven less than if the web were not treated as just explained.

A big advantage of my method and the girder produced by it is that I canuse a commercially produced prestressed top chord, instead of having toprestress at the building site. There is no waiting for concrete to setafter the girder has been assembled. There is no pre stressing to bedone after the girder have been mounted in place in the structure, ofwhich it is to form a part. The concrete top chord can be made wide andmassive enough to form a part of the floor slab. The prestressed topchords, made at a manufacturing plant, can be assembled with the web andbottom chord either at the same plant or at the location where the weband bottom chord are made. In case there are a sufficient number ofduplicate girders to be used on a given job to justify it, the assemblyof the top chords with the preassembled webs and bottom chords could bedone in assembling equipment at the job site.

Concrete is a most economical material for carrying compressivestresses, while steel is ideally suited for tension. In my girder thetwo materials are combined in their proper relationship to the greatestadvantage. Ship ment of the girder is lower in cost than the shipment ofall-concrete members, because the steel webs and bottom chords weighappreciably less than the concrete webs and bottom chords or flanges ofprecast concrete beams or girders. This reduction in weight also makesmy girder easier to handle and reduces building weights.

In the modification shown in FIGS. 8 and 9 the web 29 of the girder isformed from a steel plate that may be solid or have sections punched outof it. The concrete top chord is made and prestressed in the same way asthe one previously described, except that instead of embodying a seriesof gusset plates in the concrete 21, it is preferred to embed a singlecontinuous gusset plate 22. The lower edge of the web plate is securedby means of welding rivets or bolts to the bottom chord of the girder,which may be formed from a single member or a pair of angle bars 23. Thetop chord is laid bottom side up in tensioning apparatus similar to thatshown in FIG. 6, and stretching apparatus is secured to both ends of theinverted bottom chord and the web plate above the top chord to stretch.them. While they are under tension, the lower edge of the web plate maybe welded to the long gusset plate 22 projecting from the top chord, ora line of holes may be drilled along the lower edge of the web plate .tomatch holes previously drilled in the gusset plate. This plate and theweb then can be secured together by bolts 24 or the like. The bottomchord and web then are released fro-m the jacks and the girder isremoved from the tension-ing apparatus and may be turned right side upas shown in the drawings. The prestressed top chord of the girderprevents the stretched web and bottom chord from contractinglongitudinally. where it is desired to use a girder having an unusuallyshallow depth.

According to the provisions of the patent statutes, I have explained theprinciple of my invention and have illustrated and described what I nowconsider to represent its best embodiment. However, I desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically illustrated anddescribed.

I claim:

1. A girder comprising a prefabricated prestressed concrete top chordincluding metal gusset plate means embedded therein and projectingdownward therefrom, a prefabricated pretensioned metal bottom chordspaced from the top chord, a metal web disposed between the top andbottom chords, and means rigidly securing the top and bottom of the webto the projecting gusset plate means and to the bottom chord, the webmaintaining the bottom chord in pretensioned condition.

2. A girder according to claim 1, in which dowel rods are embedded inthe top chord transversely thereof and extend through said gusset platemeans.

3. A girder comprising a prefabricated prestressed concrete top chordincluding metal gusset plate means embedded therein and projectingdownward therefrom, a prefabricated pretensioned metal bottom chordspaced from the top chord, a longitudinally pretensioned metal web platedisposed between the top and bottom chords, and means rigidly securingthe upper and lower edges of the web plate to the projecting gussetplate means and to the bottom chord, the web plate maintaining thebottom chord in pretensioned condition.

4. A girder comprising a prefabricated prestressed concrete top chordincluding metal gusset plates embedded therein and projecting downwardtherefrom, a prefabricated pretensioned metal bottom chord spaced fromthe top chord, metal web bars disposed between the top and bottomchords, and means rigidly securing the opposite ends of said bars to thebottom chord and projecting portions of said gusset plates, some of saidbars at each side of the center of the girder being inclined from thebottom chord outwardly to the top chord and maintaining the bottom chordin pretensioned condition.

A solid web girder of this type is preferred- 5. A girder comprising aprefabricated prestressed con- 6. A girder according to filaim 5, inwhich said comcrete top chord including metal gusset plates embeddedPressl'on bars are pfestressedtherein at longitudinally spaced pointsand projecting References Cited bythe Examiner 5 1,959,119 5/1934- Young52723 XR S1011 bars and metal web compression bars disposed be-2,151,267 3/1939 Finsterwalder tween the top and bottom chords, andmeans rigidly 3,140,764 7 19 4 Cheskin 52 223 securing the opposite endsof said bars to the bottom chord and projecting portions of said gussetplates, said 10 HARRISON MOSELEY Pr'mary Examiner tension bars beingpretensioned. BELL, Assistant Examiner-

1. A GIRDER COMPRISING A PREFABRICATED PRESTRESSED CONCRETE TOP CHORDINCLUDING METAL GUSSET PLATE MEANS EMBEDDED THEREIN AND PROJECTINGDOWNWARD THEREFROM, A TOP AND BOTTOM CHORDS, AND MEANS RIGIDLY SECURINGTHE PREFABRICATED PRETENSIONED METAL BOTTOM CHORD SPACED FROM THE TOPCHORD, A METAL WEB DISPOSED BETWEEN THE